Multi-division staircase structure of three-dimensional memory device and method for forming the same

ABSTRACT

A method for forming a staircase structure of a memory device includes the following operations. A first number of divisions are formed at different depths along a first direction in a stack structure and a trench structure between adjacent divisions, the stack structure comprising interleaved sacrificial material layers and dielectric material layers. A plurality of stairs are formed along a second direction. Each of the plurality of stairs includes the first number of divisions, and each of the divisions includes a first number of sacrificial portions. The second direction is perpendicular to the first direction. An insulating portion is formed in the trench structure. A top sacrificial portion is formed on a top surface of each of the first number of divisions and in contact with the insulating portion. The top sacrificial portion is replaced with a conductor portion through a slit structure in the insulating portion and in contact with the top sacrificial portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/861,793, filed on Apr. 29, 2020, entitled “MULTI-DIVISION STAIRCASESTRUCTURE OF THREE-DIMENSIONAL MEMORY DEVICE AND METHOD FOR FORMING THESAME,” which is a continuation of International Application No.PCT/CN2020/075458, filed on Feb. 17, 2020, entitled “MULTI-DIVISIONSTAIRCASE STRUCTURE OF THREE-DIMENSIONAL MEMORY DEVICE AND METHOD FORFORMING THE SAME,” both of which are hereby incorporated by reference intheir entireties.

BACKGROUND

Embodiments of the present disclosure relate to three-dimensional (3D)memory devices and fabrication methods thereof.

Planar memory cells are scaled to smaller sizes by improving processtechnology, circuit design, programming algorithm, and fabricationprocess. However, as feature sizes of the memory cells approach a lowerlimit, planar process and fabrication techniques become challenging andcostly. As a result, memory density for planar memory cells approachesan upper limit.

A 3D memory architecture can address the density limitation in planarmemory cells. The 3D memory architecture includes a memory array andperipheral devices for controlling signals to and from the memory array.

SUMMARY

Embodiments of a multi-division staircase structure of a 3D memorydevice and method for forming the 3D memory device are disclosed herein.

In one example, a memory device includes a memory array structure and astaircase structure. The staircase structure includes a plurality ofstairs each has a first number of divisions at different depths along afirst direction. The plurality of stairs extend along a second directionperpendicular to the first direction. Each of the first number ofdivisions of a respective stair includes a conductor portion on the topsurface of the respective division and a second number of non-conductorportions under the conductor portion. The conductor portion and thenon-conductor portions are insulated from one another by one or moredielectric layers.

In another example, a memory device includes a memory array structureand a staircase structure. The staircase structure includes a pluralityof stairs each includes a first number of divisions at different depthsalong a first direction, the plurality of stairs extending along asecond direction perpendicular to the first direction. The staircasestructure also includes an insulating portion between adjacentdivisions. A depth of the insulating portion along a vertical directionis about a thickness of the respective stair. Of the insulation portion,a portion of a bottom surface in a lower adjacent division is lower thana portion of the bottom surface in a higher adjacent division.

In a further example, a method for forming a staircase structure of amemory device includes the following operations. First, a first numberof divisions are formed at different depths along a first direction in astack structure and a trench structure between adjacent divisions, thestack structure comprising interleaved sacrificial material layers anddielectric material layers. A plurality of stairs are formed along asecond direction. Each of the plurality of stairs includes the firstnumber of divisions, and each of the divisions includes a first numberof sacrificial portions. The second direction is perpendicular to thefirst direction. An insulating portion is formed in the trenchstructure. A top sacrificial portion is formed on a top surface of eachof the first number of divisions and in contact with the insulatingportion. The top sacrificial portion is replaced with a conductorportion through a slit structure in the insulating portion and incontact with the top sacrificial portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1A illustrates an exemplary 3D memory device having a staircasestructure, according to some embodiments of the present disclosure.

FIG. 1B illustrates a cross-sectional view of the 3D memory device shownin FIG. 1A, according to some embodiments of the present disclosure.

FIG. 1C illustrates another cross-sectional view of the 3D memory deviceshown in FIG. 1A, according to some embodiments of the presentdisclosure.

FIG. 2A illustrates a top front view of a 3D memory device having afour-division staircase structure in an exemplary fabrication process,according to some embodiments of the present disclosure.

FIG. 2B illustrates a cross-sectional view of the 3D memory device shownin FIG. 2A, according to some embodiments of the present disclosure.

FIG. 3A illustrates another top front view of the 3D memory device inthe exemplary fabrication process, according to some embodiments of thepresent disclosure.

FIG. 3B illustrates a cross-sectional view of the 3D memory device shownin FIG. 3A, according to some embodiments of the present disclosure.

FIGS. 4A-4F each illustrates another cross-sectional view of the 3Dmemory device in the exemplary fabrication process, according to someembodiments of the present disclosure.

FIG. 5 illustrates a flowchart of a method for forming an exemplary 3Dmemory device, according to some embodiments.

FIGS. 6A and 6B illustrate exemplary detailed fabrication operations ofthe method shown in FIG. 5, according to some embodiments.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend laterally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which interconnect lines and/or via contacts are formed) and one ormore dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND memory strings) ona laterally-oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, theterm “vertical/vertically” means nominally perpendicular to the lateralsurface of a substrate.

In some 3D memory devices, memory cells for storing data are verticallystacked through a stacked storage structure (e.g., a memory stack). 3Dmemory devices usually include staircase structures formed on one ormore sides of the stacked storage structure for purposes such as wordline fan-out. As the demand for higher storage capacity continues toincrease, the number of vertical levels of the stacked storage structurealso increases. Multi-division staircase structures have been used insome 3D NAND memory devices in which each stair (level) of the staircasestructure can have multiple divisions for fan-out multiple word linesusing the same stair, thereby reducing the interconnect layoutcomplexity and increasing the utilization of the staircase structure.

During the fabrication of the multi-division staircase structures, wordline via contacts are formed on the stairs for fan-out purposes. Theword line via contacts are often formed by forming openings in contactwith the stairs (e.g., the landing area of the stairs) in the insulatingstructure in which the staircase structure is placed, and filling theopenings with a conductive material. Conventionally, these openings,formed to be in contact with stairs at different depths/heights, areformed in the same etching process. Because of the variation in openingdepths, the openings are often not etched evenly or desirably. Forexample, the openings in contact with lower stairs (e.g., the deeperopenings) and the openings in contact with higher stairs (e.g., theshallower openings) undergo the same etching time, resulting theopenings in contact with the higher stairs to be over etched. Theover-etching can cause the top conductor layers (e.g., word lines) onthe top surfaces of the higher stairs to be undesirably damaged or evenetched through. The word line via contacts can undesirably be in contactwith the conductor layers underlying the top conductor layers, causingshort circuits in the respective divisions.

Various embodiments in accordance with the present disclosure providestructures and methods for forming a multi-division staircase structureof a 3D memory device. The multi-divisional staircase structure includesa plurality of divisions at different depths along a first direction,and a plurality of stairs extending along a second direction that isperpendicular to the first direction. Each stair includes the pluralityof divisions. In some embodiments, each division includes a topconductor portion and at least one non-conductor portion under the topconductor layer. The top conductor portion and the at least onenon-conductor portion are separated from each other by a dielectricportion in between. The top conductor portion may in contact with aconductor layer (e.g., word line) extending laterally in the staircasestructure. In some embodiments, the number of the at least onenon-conductor portion is equal to the number of divisions minus one.Adjacent non-conductor portions are separated from each other by adielectric portion. The width of each non-conductor layer along thefirst direction is the same as that of the division, and the length ofeach non-conductor layer along the second direction is the same as thatof the division (or the respective stair). In some embodiments, a wordline via contact is formed to be in contact with the top conductorportion, and the at least one non-conductor portions under therespective conductor portion may prevent any over-etching to the topconductor portion (e.g., for the formation of the opening to form theword line via contact) to cause short circuits in the 3D memory device.That is, even if the top conductor portion is damaged and/or etchedthrough, the non-conductor portions under the top conductor portion canprevent the conductive material of the word line via contact fromcontacting/interfering with other conductive structures (e.g., topconductor portions of other divisions and/or neighboring conductorlayers). In some embodiments, the non-conductor portions include siliconnitride.

In some embodiments, the staircase structure includes an insulatingportion between adjacent divisions. A contact structure electricallyconnected to the array common source (ACS) of the 3D memory deviceextends through the insulating portion. The contact structure is incontact with the top conductor portion in the higher division andisolated from the non-conductor portions in adjacent divisions. Thecontact structure is also in contact with conductor layers that arelaterally in contact with the non-conductor portions and conductorlayers under the non-conductor portions in adjacent divisions. In someembodiments, the insulating portion is formed for the formation of thenon-conductor portions and the conductor portion in each division.Specifically, the insulating portion prevents the non-conductor portionsin each division from being replaced by the conductor material duringthe gate-replacement process. The non-conductor portions can thus beretained under the respective conductor portion in the 3D memory deviceand prevent undesirable contact between the respective word line viacontact and neighboring conductive structures (e.g., other conductorlayers). The length of the insulating portion along the second directionis the same as that of the respective division (or the respectivestair), and the width of the insulating portion along the firstdirection is greater than that of the contact structure. The depth ofthe insulating portion along a vertical direction (e.g., the z-axis) issufficient for the formation of the plurality of non-conductor portionsin adjacent divisions. In some embodiments, the depth is nominally equalto the thickness of the respective stair.

FIGS. 1A, 1B, and 1C illustrate an exemplary multi-division staircasestructure of a 3D memory device, according to some embodiments. FIG. 1Ais a 3D overview of the 3D memory device, FIG. 1B is a cross-sectionalview of the 3D memory device along the A-A′ direction (e.g., the x-zplane), and FIG. 1C is a cross-sectional view of the 3D memory devicealong the B-B′ direction (e.g., the y-z plane). FIGS. 1A, 1B, and 1C aredescribed together in the present disclosure. For ease of illustration,in the present disclosure, a four-division staircase structure isdepicted and described. It should be noted that the staircase structurecan have any suitable number of divisions. For example, the number ofdivisions can be 2, 3, 4, 5, N, etc., where N representing a suitablepositive integer. The structure and method provided in this disclosurecan be employed to form a multi-division 3D memory device with anysuitable number of divisions. The specific number of divisions shouldnot be limited by the embodiments of the present disclosure.

FIG. 1A illustrates an overview of an exemplary 3D memory device 100having a staircase structure 102, according to some embodiments of thepresent disclosure. 3D memory device 100 can include a core region(“CORE REGION”) in the center and one or more staircase structures 102at the outer sides (e.g., located in “STAIRCASE REGION”). A memory arraystructure, in which a plurality of memory cells are formed, is locatedin the core region. In some embodiments, the 3D memory device is a NANDFlash memory device in which the memory cells are provided in the formof an array of NAND memory strings (not shown) in the memory arraystructure. The memory array structure can include any other suitablecomponents including, but not limited to, gate line slits (GLSs),through array contacts (TACs), array common sources (ACSs), etc.

It is noted that x and y axes are included in FIGS. 1A-1C to illustratetwo orthogonal directions in the wafer plane. In some embodiments, thex-direction is the bit line direction of 3D memory device 100, and they-direction is the word line direction of 3D memory device 100.Staircase structure 102 can be either a functional staircase structureused for landing interconnects (e.g., word line via contacts) and/ordummy channel holes or a dummy staircase structure used for balancingload in etching or chemical mechanical polishing (CMP) processes duringfabrication. The vertical direction is represented by thez-axis/direction, which is perpendicular to both x and y axes.

As shown in FIGS. 1A and 1B, staircase structure 102 may include afour-division staircase structure which includes four divisions atdifferent depths along the x-axis in each stair of staircase structure102. Staircase structure 102 may also include a plurality of stairsextending along the y-axis. Staircase structure 102 may include fourdivisions at different depths in each stair: 104A1, 104B1, 104C1, and104D1 arranged on one side of a stair 124. In some embodiments,staircase structure 102 may include four other divisions in each stair:104A2, 104B2, 104C2, and 104D2 arranged on the other side of stair 124.In some embodiments, divisions 104A1 and 104A2, 104B1 and 104B2, 104C1and 104C2, 104D1 and 104D2 are arranged symmetrically about a middleline of stair 124. In some embodiments, the middle line divides (e.g.,evenly divides) the respective stair (e.g., 124) into two portions(e.g., identical portions), each having the four divisions at differentdepths. In some embodiments, divisions 104A1 and 104A2, 104B1 and 104B2,104C1 and 104C2, 104D1 and 104D2 may respectively have the same shape,depth, dimensions, and/or depth in a respective stair. It should benoted that, in some embodiments, the two divisions that aresymmetrically distributed about the middle line of the stair and havingthe same depth are referred to as one division. However, for ease ofdescription, in the present disclosure, a division refers to the portionof a stair that is only on a single side of the middle line of thestair. Because of the symmetry of the divisions in a stair, thestructure and formation of the divisions on one side of the stair canalso be applied to those of the corresponding symmetrical divisions onthe other side of the stair. In some embodiments, the number of stairsin the x-direction is equal to or greater than 64, such as 64, 96, 128,160, 192, 224, 256, etc. For ease of depiction, only a portion ofstaircase structure 102 is shown in FIGS. 1A-1C. Staircase structure 102and the memory array structure may be formed over a substrate(“SUBSTRATE”), which can include silicon (e.g., single crystallinesilicon), silicon germanium (SiGe), gallium arsenide (GaAs), germanium(Ge), silicon on insulator (SOI), or any other suitable materials.

As shown in FIGS. 1A-1C, staircase structure 102 includes a plurality ofconductor layers 108 and a plurality of dielectric layers 112interleaved along the vertical direction (e.g., the z-axis). In someembodiments, conductor layers 108 and dielectric layers 112 extendlaterally in staircase structure 102 and into the core region. Conductorlayers 108 can include conductive materials including, but not limitedto, tungsten (W), cobalt (Co), copper (Cu), aluminum (Al),polycrystalline silicon (polysilicon), doped silicon, silicides, or anycombination thereof. Dielectric layers 112 can include dielectricmaterials including, but not limited to, silicon oxide, silicon nitride,silicon oxynitride, or any combination thereof. In some embodiments,conductor layers 108 include metals, such as tungsten, and dielectriclayers 112 include silicon oxide. Along the z-axis, the thicknesses ofconductor layers 108 and dielectric layers 112 may be the same ordifferent.

In some embodiments, staircase structure 102 includes four divisions104A1, 104B1, 104C1, and 104D1 at different depths arranged along thex-axis on one side of the respective stair, and another four divisions104A2, 104B2, 104C2, and 104D2 at different depths arrangedsymmetrically along the x-axis on the other side of the respectivestair. In some embodiments, stairs in the same division extend along they-axis. A contact structure 132, conductively connected to the ACS of 3Dmemory device 100, may be positioned between adjacent divisions. Forease of depiction, contact structures 132 are not shown in FIGS. 1A and1C, but shown in FIG. 1B. In some embodiments, contact structure 132extends vertically into the substrate and laterally into the coreregion. Contact structure 132 may include an insulating spacer and acontact extending in the insulating spacer. The insulating spacer mayinclude dielectric materials including, but not limited to, siliconoxide, silicon nitride, silicon oxynitride, or any combination thereof.The contact may include conductive materials including, but not limitedto, tungsten, cobalt, copper, aluminum, polysilicon, doped silicon,silicides, or any combination thereof. In some embodiments, 3D memorydevice 100 includes an insulating structure 134 (shown only in FIG. 1Bfor ease of depiction) in which staircase structure 102 is positioned.Insulating structure 134 may include dielectric materials including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride, orany combination thereof.

For ease of illustration, the details of staircase structure 102 isfurther described in view of two consecutive stairs 124 and 125 shown inFIGS. 1A-1C. Each stair (e.g., 124 or 125) may include four divisions104A1, 104B1, 104C1, and 104D1 at different depths arranged along thex-axis on one side of the respective stair, and another four divisions104A2, 104B2, 104C2, and 104D2 at different depths arrangedsymmetrically along the x-axis on the other side of the respectivestair. An insulating portion 106 may be positioned between adjacentdivisions of each stair (e.g., 124 or 125). Contact structure 132 mayextend through insulating portion 106. In some embodiments, anotherinsulating portion (e.g., 118), aligned with the middle line of therespective stair (e.g., 124), is positioned between divisions 104A1 and104A2.

In each division, staircase structure 102 may include a conductorportion (e.g., a top conductor portion) at the top surface andfunctioning as the landing area for word line via contacts, and anon-conductor structure under the respective conductor portion. Forexample, in division 104A2 of stair 124, a conductor portion 108-1 ispositioned on the top surface and a non-conductor structure 114 ispositioned under conductor portion 108-1. Conductor portion 108-1 andnon-conductor structure 114 may be insulated from each other by adielectric portion 112-1. In each division, each conductor portion 108-1is in contact with a respective conductor layer 108 extending from thestaircase region to the core region, and each dielectric portion 112-1is in contact with a respective dielectric layer 112 extending from thestaircase region to the core region. In some embodiments, dielectricportions 112-2 include the same material(s) as dielectric layers 112.

In some embodiments, each division includes a conductor portion 108-1 incontact with a respective conductor layer 108. Conductor portion 108-1and conductor layer 108 may include the same material(s). Non-conductorstructure 114 may include a plurality of non-conductor portions 110arranged under the respective conductor portion 108-1. In someembodiments, non-conductor structure 114 includes the same number ofnon-conductor portions 110 and dielectric portions 112-1, interleavedwith one another along the z-axis. In some embodiments, along thex-axis, a width W_(C) of conductor portion 108-1 is equal to or greaterthan a width W_(N) of non-conductor structure 114. In some embodiments,W_(C) is greater than W_(N) along the x-axis. In some embodiments, alongthe x-axis, widths of all non-conductor portions 110 are nominally thesame and equal to W_(N). In some embodiments, along the y-axis, a lengthof conductor portion 108-1 is nominally equal to a length ofnon-conductor structure 114. The length L may be nominally equal to alength of the respective stair (e.g., 124 or 125). In some embodiments,the width (along the x-axis) and the length (along the y-axis) ofdielectric portion 112-1 are nominally the same as those ofnon-conductor portions 110.

In some embodiments, in each division, a number non-conductor portions110 (e.g., 3) is equal to a number of divisions (e.g., 4). For example,the number of divisions may be any suitable positive integer such as 2,3, 4, 5, . . . , etc., and the number of non-conductor portions in eachdivision of a respective stair (e.g., 124 or 125) may be 1, 2, 3, 4, . .. etc. The number of divisions is referred to as the first number, andthe number of non-conductor portions 110 is referred to as the secondnumber. Non-conductor portions 110 may include any suitable dielectricmaterial that is different from dielectric portions 112-1 (or dielectriclayers 112). In some embodiments, non-conductor portions 110 includessilicon nitride (SiN). The thickness of non-conductor portion 110 may bethe same as or different from the thickness of dielectric portions112-1. In some embodiments, each non-conductor portion 110 is in contactwith a conductor layer 108 that extends on the same level. That is,non-conductor structure 114 (or non-conductor portions 110) may be incontact with a second number of conductor layers 108, each being on thesame level with the respective non-conductor portion 110. Similarly,non-conductor structure 114 may be in contact with a second number ofdielectric layers 112, each being on the same level with the respectivedielectric portion 112-1.

Insulating portion 106 may be located between adjacent divisions, e.g.,between divisions 104A2 and 104B2, 104A1 and 104B1, etc. In someembodiments, along the x-axis, a width D of insulating portion 106 isgreater than a width d of a respective contact structure. In someembodiments, D is sufficiently large to prevent contact between contactstructure 132 and adjacent non-conductor portions 110. In someembodiments, D is in a range of about 200 nm to about 400 nm, and d isin a range of about 120 nm to about 160 nm. In some embodiments, alongthe vertical direction, a depth t of insulating portion 106 is about (orat least equal to) the thickness of the respective stair (e.g., 124). Atop surface of insulating portion 106 may be in contact with the bottomsurface of conductor portion 108-1 in the higher division. A bottomsurface of insulating portion 106 may be in contact with (e.g.,extending into) dielectric portions 112-1 immediately under the bottomnon-conductor portions 110 in adjacent divisions. For example, thicknesst of insulating portion 106 between divisions 104A2 and 104B2 is equalto or greater than a thickness of stair 124 in division 104B2. That is,thickness t of insulating portion 106 between divisions 104A2 and 104B2may be at least a total thickness from the top surface of conductorportion 108-1 to the bottom surface of the bottom non-conductor portions110 in division 104B2 (e.g., the lower division). In some embodiments,the top surface of insulating portion 106 extends above the top surfaceof conductor portion 108-1 in division 104B2 (e.g., the lower division).In some embodiments, the top surface of insulating portion 106 is incontact with the bottom surface of conductor portion 108-1 in division104A2 (e.g., the higher division). The bottom surface of insulatingportion 106 may be in contact with dielectric portions 112-1 immediatelyunder the bottom non-conductor portion 110 in divisions 104A2 and 104B2.In some embodiments, along the y-axis, a length of insulating portion106 is nominally equal to L. In some embodiments, of the bottom surfaceof insulating portion 106, the portion in the higher division (e.g.,104A2) is higher than the portion in the portion in the lower division(e.g., 104B2).

As shown in FIGS. 1A-1C, except for contact structure 132 betweendivisions 104A1 and 104A2 (e.g., two divisions of equal depth), eachcontact structure 132 is in contact with conductor portion 108-1 of ahigher division. In some embodiments, contact structure 132 has nocontact with non-conductor portions 110 of each of the adjacentdivisions. For example, contact structure 132 between divisions 104A2and 104B2 is in contact with conductor portion 108-1 of division 104A2,and has no contact with non-conductor portions 110 in divisions 104A2and 104B2. In some embodiments, each contact structure 132 is in contactwith a plurality of conductor layers 108 under the respective insulatingportion 106 (or under the respective adjacent divisions). For example,contact structure 132 between divisions 104A2 and 104B2 is in contactwith conductor layers 108 under divisions 104A2 and 104B2, and contactstructure 132 between divisions 104B2 and 104C2 is in contact withconductor layers 108 under divisions 104C2 and 104B2.

In some embodiments, in the same division, conductor portion 108-1 of alower stair is in contact with and conductively connected to conductorlayer 108 immediately under non-conductor structure 114 of a higherstair. For example, as shown in FIG. 1B, in division 104A2, conductorlayer 108 immediately under non-conductor structure 114 (or the bottomdielectric layer 112 of non-conductor structure 114) in stair 124 is incontact with and conductively connected to conductor portion 108-1 instair 125. In some embodiments, in each division, the three conductorlayer 108 immediately under conductor layer 108 are in contact with therespective non-conductor portions 110 in the respective stair. Forexample, in division 104A2, the three conductor layers 108 immediatelyunder conductor layer 108 are respectively in contact with the threenon-conductor portions 110 in stair 125.

In some embodiments, 3D memory device 100 includes another insulatingportion 118 between divisions 104A1 and 104A2. In some embodiments, atop surface of insulating portion 118 is nominally coplanar with topsurfaces of conductor portions 108-1 of divisions 104A1 and 104A2, and abottom surface of insulating portion 118 is at least in contact withdielectric layers 112 under the bottom non-conductor portions 110 indivisions 104A1 and 104A2. In some embodiments, a depth of insulatingportion 118 is less than or equal to the thickness of stair 124. In someembodiments, a width of insulating portion 118 along the x-axis and alength of insulating portion 118 along the second direction are similaror the same as insulating portion 106. In various embodiments, thethicknesses of insulating portions 106 and 118 vary, depending on thefabrication process. For example, the depths of insulating portions 106and 118 can be greater than, equal to, or less than the thickness of therespective stair. As described earlier, in each stair, the depthsinsulating portions 106 and 118 can be any suitable value to form asecond number of non-conductor portions 110 to be formed under therespective conductor portion 108-1 in adjacent divisions.

In some embodiments, contact structure 132 extends through insulatingportion 118, between divisions 104A1 and 104A2, and is in contact withand conductively connected to conductor layers 108 in divisions 104A1and 104A2 of a lower stair (e.g., stair 125). In some embodiments, asshown in FIG. 1B, contact structure 132 between two adjacent divisionsis in contact with any conductor layers 108 under the two adjacentdivisions of the respective stair. In some embodiments, in each stair,contact structure 132 between the two adjacent divisions is in contactwith a first number of conductor layers 108 in contact with each of theadjacent divisions. For example, as shown in FIGS. 1A-1C, in stair 124,contact structure 132 between adjacent divisions 104A2 and 104B2 are incontact with conductor layers 108 that are in contact with conductorportion 108-1 and the three (e.g., the second number of) non-conductorportions 110 in each of divisions 104A2 and 104B2.

FIGS. 2A and 2B, 3A and 3B, and 4A-4F illustrate the structure of astaircase structure at different stages during an exemplary fabricationprocess, according to some embodiments. FIG. 5 illustrates a flow chartof the fabrication process shown in FIGS. 2A and 2B, 3A and 3B, and4A-4F. FIGS. 6A and 6B illustrate detailed fabrication operations of themethod shown in FIG. 5. FIG. 6B is a continuation of FIG. 6A. It isunderstood that the operations shown in method 500 are not exhaustiveand that other operations can be performed as well before, after, orbetween any of the illustrated operations. Further, some of theoperations may be performed simultaneously, or in a different order thanthose shown in FIGS. 5 and 6.

As shown in FIG. 5, at the beginning of the process, at Operation 502,in a stack structure, a first number of divisions at different depthsalong a first direction and a trench structure is formed betweenadjacent divisions are formed. The stack structure has interleavedsacrificial material layers and dielectric material layers is formed.FIGS. 2A, 2B, 3A, and 3B illustrate corresponding structures.

FIG. 2A illustrates a 3D overview of a stack structure 202, according tosome embodiments. FIG. 2B illustrates a cross-sectional view of stackstructure 202 along the C-C′ direction (e.g., the x-z plane). As shownin FIG. 2A, stack structure 202 may be a dielectric stack and mayinclude a plurality of dielectric material layers 211 and sacrificialmaterial layers 212, arranged alternatingly along the z-axis. Dielectricmaterial layers 211 and sacrificial material layers 212 may includedifferent materials. Each dielectric material layer 211 and theunderlying sacrificial material layer 212 can be referred to as a“dielectric pair”, and vice versa. In some embodiments, dielectricmaterial layers 211 and sacrificial material layers 212 arealternatingly deposited above a substrate (e.g., a silicon substrate).In some embodiments, each dielectric material layer 211 includes a layerof silicon oxide, and each sacrificial material layer includes a layerof silicon nitride. Stack structure 202 can be formed by one or morethin film deposition processes including, but not limited to, chemicalvapor deposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), or any combination thereof.

According to Operation 602, a first number of division patterns areformed at different depths along a first direction in the stackstructure. As shown in FIGS. 2A and 2B, a staircase division pattern(SDP) can be formed on stack structure 202. The SDP may divide stackstructure 202 into four division patterns 204A, 204B, 204C, and 204D atdifferent depths along the x-axis (e.g., the first direction). In eachdivision pattern, dielectric material layer 211 may be over sacrificialmaterial layer 212. The four division patterns 204A, 204B, 204C, and204D can be formed by a plurality of cycles of trimming an etch masklaterally (e.g., along the x and y axes) and etching a part of stackstructure 202 exposed by the etch mask. In some embodiments, three SDPmasks are used to form the four division patterns. For example, a firstSDP mask may cover a portion of stack structure 202 and expose the areacorresponding to division pattern 204D. A suitable etching process(e.g., a first etching process), such as a dry etch and/or a wet etch,can be performed subsequently to remove a portion of stack structure 202exposed by the first SDP mask. In some embodiments, the amount ofmaterials removed by the etching process has a thickness of a stairdepth, e.g., nominally equal to a dielectric pair (e.g., the totalthickness of one dielectric material layer 211 and the underlyingsacrificial material layer 212). A second SDP mask can be formed bytrimming the first SDP mask inwardly and incrementally along the x-axisand the y-axis, to expose the area corresponding to division patterns204D and 204C. A second etching process similar to the first etchingprocess can be subsequently performed to remove a portion of (e.g., astair depth of) stack structure 202 exposed by the second SDP mask. Theetch pattern on stack structure 202, formed by the first etchingprocess, can be transferred by the second etching process. A third SDPmask can be formed by trimming the second SDP mask inwardly andincrementally along the x-axis and the y-axis, to expose the areacorresponding to division patterns 204D, 204C, and 204B. A third etchingprocess similar to the first and second etching process can besubsequently performed to remove a portion of (e.g., a stair depth of)stack structure 202 exposed by the third SDP mask. The etch pattern onstack structure 202, formed by the first and second etching processes,can be transferred by the third etching process. In some embodiments,the shapes of the three SDP masks are nominally rectangular. In someembodiments, the three SDP masks may include hard etch masks and/or softetch masks. The hard etch masks can be formed by patterning a hardmaterial such as carbon using a patterned photoresist layer, formed bycoating a photoresist layer followed by a photolithography process. Thesoft etch masks can include a patterned photoresist layer, formed bycoating a photoresist layer followed by a photolithography process.

FIG. 3A illustrates a 3D overview of a stack structure 202, according tosome embodiments. FIG. 3B illustrates a cross-sectional view of stackstructure 202 along the C-C′ direction (e.g., the x-z plane). Accordingto Operation 604, a trench structure is formed between adjacentdivisions to form a first number of divisions at different depths alongthe first direction. As shown in FIGS. 3A and 3B, a trench structure 306is formed between adjacent divisions to divide division pattern 204A,204B, 204C, and 204D into four divisions 204A1, 204B1, 204C1, and 204D1of different depths on one side (e.g., along the x-axis) of stackstructure 202, and four divisions 204A2, 204B2, 204C2, and 204D2 ofdifferent depths on the other side (e.g., along the x-axis) of stackstructure. In some embodiments, trench structure 306 dividing divisionpattern 204A into divisions 204A1 and 204A2 is aligned with the middleline (e.g., along the x-axis) of stack structure 202, and divides stackstructure 202 into nominally symmetrical portions along the x-axis.

Referring back to FIG. 2B, trench structure 306 can be formed betweenadjacent divisions, e.g., between adjacent division patterns and alongthe middle line (e.g., along the x-axis) of stack structure 202. In FIG.2B, areas I and II may each represent an area in adjacentdivisions/division patterns in which trench structure 306 can be formed.As an example shown in FIG. 2B, area I represents the area in division204B2 or division pattern 204B, and area II represents the area indivision 204A2 or division pattern 204A. The widths of areas I and IImay each be at least the width of trench structure 306 along the x-axis.For example, the width of each of area I and II along the x-axis caneach be in a range of about 200 nm to about 400 nm. In some embodiments,trench structure 306 is entirely formed in one of areas I and II. Insome embodiments, trench structure 306 is partially formed in each ofareas I and II. In some embodiments, trench structure 306 is formed by asuitable patterning process, e.g., a dry etch and/or a wet etch process.

As shown in FIG. 3A, trench structure 306 may be formed to extendlaterally along the y-axis in stack structure 202. In some embodiments,along the y-axis, a length of trench structure 306 may be nominallyequal to the length of stack structure 202. As shown in FIG. 3B, anetching profile of trench structure 306 may form four (e.g., the firstnumber of) initial sacrificial layers 312, formed from the etching ofinitial sacrificial layers 312, in each adjacent division. The fourinitial sacrificial layers 312 may be exposed on the sidewall of trenchstructure 306. In some embodiments, in each division, each initialsacrificial layer 312 is sandwiched by an initial dielectric layer 311,which is formed from the etching of sacrificial material layers 212 andhas nominally the same shape as the respective initial sacrificiallayers 312 along the x and y axes. In some embodiments, when trenchstructure 306 is formed between two adjacent divisions at differentdepths (e.g., between divisions 204A2 and 204B2), the etching profile oftrench structure 306 is asymmetric along the x-axis, as shown in FIG.3B, to form four initial sacrificial layers 312 in each adjacentdivision. For example, the bottom surface of trench structure 306 can beshallower on the side of the higher division (e.g., division 204A2) tobe in contact with initial dielectric layer 311 underlying the fourth(e.g., lowest) initial sacrificial layer 312 in division 204A2. Also,the bottom surface of trench structure 306 can be deeper on the side ofthe lower division (e.g., division 204B2) to be in contact with initialdielectric layer 311 underlying the fourth (e.g., lowest) initialsacrificial layer 312 in division 204B2. In some embodiments, for trenchstructure 306 between divisions at the same depth (e.g., trenchstructure 306 between divisions 204A1 and 204A2), the etching profile oftrench structure 306 is nominally even on both sides of the divisions(e.g., 204A1 and 204A2) to form four initial sacrificial layers 312 ineach division. In some embodiments, initial dielectric layer 311 underthe fourth (e.g., lowest) initial sacrificial layer 312 of each divisionare partially etched or entirely etched along the z-axis. In someembodiments, along the x-axis, a width D of trench structure 306 is in arange of about 200 nm to about 400 nm.

Referring back to FIG. 5, after the formation of trench structures,method 500 proceeds to Operation 504, in which a plurality of stairs areformed along a second direction, each of the stairs having the firstnumber of divisions, and each of the divisions having the first numberof sacrificial portions.

According to Operation 606, a plurality of stairs extending along they-axis (e.g., the second direction) can be formed in stack structure202, referring back FIGS. 1A and 1C. Each of the stairs may include thefirst number of divisions, and each of the divisions includes the firstnumber of sacrificial portions. The formation of the stairs may includerepetitive etching of stack structure 202 using an etch mask (e.g., apatterned photoresist or PR layer) over stack structure 202. The etchmask can be repetitively trimmed inwardly and incrementally, often fromall directions, to expose the portions of stack structure 202 to beetched. The amount of trimmed PR can be directly related (e.g.,determinant) to the dimensions of the stairs. For example, the amount oftrimmed PR along the y-axis may determine the length of a stair alongthe y-axis. The trimming of the PR layer can be obtained using asuitable etch, e.g., an isotropic dry etch such as a wet etch. One ormore PR layers can be formed and trimmed consecutively for the formationof the stairs. In some embodiments, the etching of stack structure 202,e.g., using a suitable etching process such as dry etch and/or wet etch,follows the trimming of the PR layer. In some embodiments, stackstructure 202 is etched by a second stair depth along the z-axisfollowing each trimming of the PR layer. The second stair depth may beequal to the total thickness of four (e.g., the first number of)dielectric pairs (e.g., the top four initial dielectric/sacrificiallayer pairs) along the z-axis. The trimming process of a photoresistmask followed by the etching process of a stack structure is referred toherein as a trim-etch cycle. The number of trim-etch cycles candetermine the number of stairs formed in stack structure 202 along they-axis. In some embodiments, after the formation of stairs, dielectricmaterial layers 211 may form sacrificial layers (e.g., 423 shown in FIG.4A), and dielectric material layers may form dielectric layers (e.g.,424 shown in FIG. 4A).

In some embodiments, the etch profile of trench structures 306, formedbefore the formation of stairs, is transferred onto the formed staircasestructure such that each stair includes four divisions 204A1-204D1 andother four divisions 204A2-204D2. Each of the two adjacent divisions areseparated from each other by trench structure 306. In some embodiments,the etch profile of trench structure 306 remains nominally the sameafter the formation of the stairs. For ease of illustration, in arespective stair, trench structure 306 may form four (e.g., the firstnumber of) sacrificial portions (e.g., 412 in FIG. 4A) in each division.Each of the sacrificial portion may be sandwiched by a pair ofdielectric portions (e.g., 411 in FIG. 4A). The lateral area of eachsacrificial portion and each dielectric portion (e.g., along the x-yplane) may be determined by the dimension of the respective divisionalong the x-axis and the dimension of the respective stair along they-axis. Each sacrificial portion may be in contact with a sacrificiallayer of the same level and extending laterally in stack structure 202,and each dielectric portion may be in contact with a dielectric layer ofthe same level and extending laterally in stack structure 202.

In various embodiments, Operation 502 can be performed before or afterOperation 504. In some embodiments, the stairs are formed before theformation of divisions. For example, the plurality of stairs are formedalong the y-axis prior to the formation of division patterns anddivisions along the x-axis. The fabrication process of this order can bereferred to the description above and is not repeated herein. The actualorder to form the stairs and the divisions should be determined based onthe fabrication process and not be limited by the embodiments of thepresent disclosure.

Referring back to FIG. 5, after the formation of stairs, method 500proceeds to Operation 506, in which an insulating portion is formed ineach trench. FIGS. 4A and 4B illustrate a corresponding structure.

According to Operation 608, a layer of dielectric material is depositedto fill the trench structures. As shown in FIGS. 4A and 4B, a layer 404of dielectric material may be deposited to fill in trench structures306. The dielectric material may also be on the first dielectric portion411 at the top surface of each division. According to Operation 610, thefirst dielectric portion and the deposited dielectric material areremoved to expose the first sacrificial portion in each division. Insome embodiments, after trench structures 306 are filled with thedielectric material, a suitable etching process is performed to removedielectric portion 411 in each division and any dielectric material ondielectric portion 411, to expose the first sacrificial portion 412 ineach division of a stair 324. In some embodiments, a top surface and aside surface of sacrificial portion 412 are exposed in each division ofstair 324. In some embodiments, the side surface of sacrificial portion412 refers to the side surface facing away from the middle line of thestair 324. Insulating portions 406 and 418 can be formed betweenadjacent divisions. In some embodiments, for insulating portions 406that are each located between two adjacent divisions of differentdepths, a top surface of insulating portion 406 is above the top surfaceof sacrificial portion 412 in a lower division and below the top surfaceof sacrificial portion 412 in a higher division. That is, the topsurface of insulating portion 406 is between the top surfaces ofrespective adjacent divisions. In some embodiments, for insulatingportion 418 located between two adjacent divisions of nominally the samedepth, a top surface of insulating portion 418 is nominally coplanarwith sacrificial portions 412 in adjacent divisions. In someembodiments, stack structure 202 includes a plurality of interleavedsacrificial layers 424 and dielectric layers 423 under stair 324.Sacrificial layers 424 may be in contact with sacrificial portions inlower stairs, and dielectric layers 423 may be in contact withdielectric portions in lower stairs.

In some embodiments, the dielectric material includes any suitabledielectric materials such as silicon oxide. In some embodiments, thedeposition of silicon oxide includes, but not limited to, CVD, PVD, andALD. In some embodiments, the removal of the dielectric materialincludes a suitable etching process such as dry etch and/or wet etch.

Referring back to 5, after the formation of insulating portions, method500 proceeds to Operation 508, in which a top sacrificial portion isformed on the top surface of each division and in contact with therespective insulating portion. FIGS. 4C and 4D illustrate correspondingstructures.

According to Operation 612, a layer of sacrificial material is depositedon the first sacrificial portions and the insulating portions. As shownin FIG. 4C, a layer 410 of sacrificial material can be deposited on atleast the exposed first sacrificial portions 412 in stack structure 202.Layer 410 may also be in contact with (e.g., cover) the exposed sidesurface of the first sacrificial portion 412 and the top surface of eachinsulating portion 406 such that each insulating portion 406 can beconnected to the first sacrificial portion of the adjacent higherdivision through the sacrificial material. According to Operation 614, aportion of the deposited dielectric material on at least a sidewall ofeach insulating portion is removed to form a plurality of topsacrificial portions. As shown in FIG. 4D, a portion of layer 410 on thesidewall of each insulating portion 106 may be removed to disconnect thedeposited sacrificial material between adjacent divisions. In someembodiments, in stair 324, a portion of layer 410 partially or fullycovers the top and side surfaces of the first sacrificial portion 412 ofeach division and the top surface of the respective insulating portion106, which is positioned between the respective division and a lowerdivision. For example, the portion of layer 410 may partially or fullycover the top and side surfaces of first sacrificial portion 412 ofdivision 204B2 and the top surface of insulating portion 406 betweendivisions 204B2 and 204C2. In some embodiments, a portion of layer 410on the top surface of stack structure 202 (or stair 324) is removed. Insome embodiments, insulating portion 418 is exposed on the top surfaceof stack structure 202 (e.g., between divisions 204A1 and 204A2).

Each portion of layer 410 and the underlying first sacrificial portion412 may be referred to as a top sacrificial portion 420, at the topsurface of each division of stair 324. In some embodiments, because awidth of the top sacrificial portion 420, along the x-axis, includes thewidth of first sacrificial portion 412 and at least a part of the widthof insulating portion 106, the width of the sacrificial portion 420 isgreater than widths of the underlying sacrificial portions 412. In someembodiments, in stair 324, top sacrificial portions 420 of each division(e.g., 204A1-D1, 204A2-D2) are separated from one another.

In some embodiments, the sacrificial material includes a dielectricmaterial the same as sacrificial material layers 212, such as siliconnitride. In some embodiments, the deposition of silicon nitrideincludes, but not limited to, CVD, PVD, and ALD. In some embodiments,the removal of the sacrificial material includes a suitable etchingprocess such as dry etch and/or wet etch.

Referring back to FIG. 5, after the formation of top sacrificialportions, method 500 proceeds to Operation 510, in which the topsacrificial portion is replaced with a conductor portion through a liststructure in the insulating portion and in contact with the topsacrificial portion. FIGS. 4E and 4F illustrate correspondingstructures.

According to Operation 616, a slit structure is formed in a respectiveinsulating portion. As shown in FIG. 4E, a plurality of slit structures426 and 428 are formed in stack structure 202, each extending verticallyin the respective insulating portion and laterally along the y-axis. Insome embodiments, slit structures 426 and 428 may extend into thesubstrate. In some embodiments, slit structure 426 is formed ininsulating portion 406, and slit structure 428 is formed insulatingportion 418. A width d of each of slit structures 426 and 428 may be ina range of about 120 nm to about 160 nm, less than width D of insulatingportions 406 and 418, which is in a range of about 200 nm to about 400nm. Thus, each slit structure 426 may be in contact with top sacrificialportion 420 in a higher adjacent division of stair 324 and have nocontact with the three sacrificial portions 412 underlying topsacrificial portion 420. In some embodiments, slit structure 426 is incontact with the sacrificial material over the respective insulatingportion 406. In some embodiments, slit structure 426 may be in contactwith sacrificial layers 424 under sacrificial portions 412 of adjacentdivisions and sacrificial layers 424 in contact with top sacrificialportion 420 and sacrificial portions 412 on the same levels. In someembodiments, slit structure 418 has no contact with sacrificial portions412 and top sacrificial portions 420 in adjacent divisions, and is incontact with sacrificial layers 424 under sacrificial portions 412 ofadjacent divisions and sacrificial layers 424 in contact with topsacrificial portion 420 and sacrificial portions 412 on the same levels.In some embodiments, an insulating structure 430 is formed to surroundstack structure 202 such that stack structure 202 is in insulatingstructure 430. In some embodiments, insulating structure 430 is formedprior to the formation of slit structures 426.

In some embodiments, slit structures 426 and 428 are formed by anysuitable patterning process, e.g., a dry etch and/or a wet etch. In someembodiments, insulating structure 430 includes silicon oxide and isdeposited by one or more of CVD, PVD, and ALD.

According to Operation 618, the top sacrificial portion and othersacrificial layers in contact with the slit structure are replaced witha respective top conductor portion and a plurality of conductor layers.As shown in FIG. 4F, a conductor portion 408 may be formed at the topsurface of each division in stair 324. In some embodiments, sacrificiallayers 424 in contact with a slit structure, e.g., 426 or 428, arereplaced with a conductor layer 414. In some embodiments, a suitableisotropic etching process, e.g., a wet etch, is performed through slitstructures 426 and 428 to remove the sacrificial materials in topsacrificial portions 420 and any sacrificial layers 424 that are incontact with slit structures 426 and 428 to form a plurality of lateralrecesses. In some embodiments, a top lateral recess is formed in eachdivision as a result of the removal of top sacrificial portion 420. Asuitable conductor material, such as tungsten, can be deposited into thelateral recesses by a deposition process that includes, but not limitedto, CVD, ALD, and PVD. Conductor portion 408 may be formed in eachdivision. A plurality of conductor layers 414 under each division and asecond number of (e.g., three) conductor layers 414 may be formed incontact with the second number of sacrificial portions 412. Because thesecond number of sacrificial portions 412 have no contact with slitstructures 426 and 428, the sacrificial material in sacrificial portions412 is retained after the etching and the gate-replacement process. Thethree sacrificial portions 412 and the respective underlying dielectricportions 411 may form a non-conductor structure (e.g., 114 in FIG. 1C)under the respective conductor portion 408 in each division. Eachsacrificial portion 412 may be referred to as a non-conductor portion.

According to Operation 620, a contact structure is formed in the slitstructure. In some embodiments, a contact structure 432 is formed ineach slit structure. Except for contact structure 432 between divisions204A1 and 204A2, each contact structure 432 is in contact with conductorportion 408 in a higher adjacent division. For example, contactstructure 432 between divisions 204A2 and 204B2 is in contact withconductor portion 408 of division 204A2. In some embodiments, contactstructure 432 between divisions 204A1 and 204A2 is not in contact withconductor portions 408 of adjacent divisions (e.g., divisions 204A1 and204A2). In some embodiments, conductor portion 432 is also in contactwith a plurality of conductor layers 414 under adjacent divisions, and asecond number of (e.g., three) conductor layers in contact with thesecond number of sacrificial portions 412 (or the non-conductorportions) in each adjacent divisions.

In some embodiments, contact structure 432 includes an insulating spacerand a contact in the insulating spacer. The insulating spacer mayinclude silicon oxide and can be formed by at least one of ALD, CVD, andPVD. The contact may include tungsten and can be formed by at least oneof ALD, CVD, and PVD. In some embodiments, contact structure 432 alsoincludes a doped region in the substrate and in contact with thecontact. The doped region can be formed prior to the formation of thecontact and can be formed by a suitable doping process such as ionimplantation.

According to embodiments of the present disclosure, a memory deviceincludes a memory array structure and a staircase structure. Thestaircase structure includes a plurality of stairs each has a firstnumber of divisions at different depths along a first direction. Theplurality of stairs extend along a second direction perpendicular to thefirst direction. Each of the first number of divisions of a respectivestair includes a conductor portion on the top surface of the respectivedivision and a second number of non-conductor portions under theconductor portion. The conductor portion and the non-conductor portionsare insulated from one another by one or more dielectric layers.

In some embodiments, in each of the first number of divisions, a lengthof each of the second number of non-conductor portions along the seconddirection is the same as a length of the respective stair along thesecond direction.

In some embodiments, the memory device further includes an insulatingportion between adjacent divisions. A length of the insulating portionalong the second direction is the same as the length of the respectivestair, and a depth of the insulating portion along a vertical directionis about a thickness of the respective stair.

In some embodiments, the memory device further includes a contactstructure extending in the insulating portion between the adjacentdivisions. Along the first direction, a width of the insulating portionis greater than a width of the contact structure such that the contactstructure is separated from the second number of non-conductor portionsin the adjacent divisions.

In some embodiments, the width of the insulating portion along the firstdirection is in a range of about 200 nm to about 400 nm.

In some embodiments, the second number is equal to the first numberminus one.

In some embodiments, each of the first number of divisions furtherincludes one or more conductor layers under the second number ofnon-conductor portions and extending along the second direction.

In some embodiments, each of the first number of divisions furtherincludes a second number of conductor layers respectively in contactwith the second number of non-conductor portions and extending along thesecond direction.

In some embodiments, the contact structure is in contact with (i) theconductor portion in a higher adjacent division, (ii) the one or moreconductor layers under the second number of non-conductor portions, and(iii) the second number of conductor layers in contact with the secondnumber of non-conductor portions. In some embodiments, the contactstructure is isolated from the non-conductor portions in adjacentdivisions.

In some embodiments, the memory device further includes, in therespective stair, another first number of divisions arrangedsymmetrically of the first number of divisions about a middle line ofthe stair; another insulating portion extending vertically along themiddle line of the stair; and another contact structure extending in theother insulating portion. The other contact structure is separated fromthe conductor portion and the second number of non-conductor portions ineach of the adjacent divisions.

According to embodiments, a memory device includes a memory arraystructure and a staircase structure. The staircase structure includes aplurality of stairs each includes a first number of divisions atdifferent depths along a first direction, the plurality of stairsextending along a second direction perpendicular to the first direction.The staircase structure also includes an insulating portion betweenadjacent divisions. A depth of the insulating portion along a verticaldirection is about a thickness of the respective stair. Of theinsulation portion, a portion of a bottom surface in a lower adjacentdivision is lower than a portion of the bottom surface in a higheradjacent division.

In some embodiments, a length of the insulating portion along the seconddirection is the same as the length of the respective stair.

In some embodiments, each of the first number of divisions of arespective stair includes a conductor portion on the top surface of therespective division and a second number of non-conductor portions underthe conductor portion. The conductor portion and the non-conductorportions may be insulated from one another by one or more dielectriclayers.

In some embodiments, in each of the first number of divisions, a lengthof each of the second number of non-conductor portions along the seconddirection is the same as a length of the respective stair along thesecond direction.

In some embodiments, the memory device further includes a contactstructure extending in the insulating portion between the adjacentdivisions. Along the first direction, a width of the insulating portionis greater than a width of the contact structure such that the contactstructure is separated from the second number of non-conductor portionsin the adjacent divisions.

In some embodiments, the width of the insulating portion along the firstdirection is in a range of about 200 nm to about 400 nm.

In some embodiments, the second number is equal to the first numberminus one.

In some embodiments, each of the first number of divisions furtherincludes one or more conductor layers under the second number ofnon-conductor portions and extending along the second direction.

In some embodiments, each of the first number of divisions furtherincludes a second number of conductor layers respectively in contactwith the second number of non-conductor portions and extending along thesecond direction.

In some embodiments, the contact structure is in contact with (i) theconductor portion in a higher adjacent division, (ii) the one or moreconductor layers under the second number of non-conductor portions, and(iii) the second number of conductor layers in contact with the secondnumber of non-conductor portions. In some embodiments, the contactstructure is isolated from the non-conductor portions in adjacentdivisions.

In some embodiments, the memory device further includes, in therespective stair, another first number of divisions arrangedsymmetrically of the first number of divisions about a middle line ofthe stair, another insulating portion extending vertically along themiddle line of the stair; and another contact structure extending in theother insulating portion, wherein the other contact structure isseparated from the conductor portion and the second number ofnon-conductor portions in each of the adjacent divisions.

According to the embodiments of the present disclosure, a method forforming a staircase structure of a memory device includes the followingoperations. First, a first number of divisions are formed at differentdepths along a first direction in a stack structure and a trenchstructure between adjacent divisions, the stack structure havinginterleaved sacrificial material layers and dielectric material layers.A plurality of stairs are formed along a second direction. Each of theplurality of stairs includes the first number of divisions, and each ofthe divisions includes a first number of sacrificial portions. Thesecond direction is perpendicular to the first direction. An insulatingportion is formed in the trench structure. A top sacrificial portion isformed on a top surface of each of the first number of divisions and incontact with the insulating portion. The top sacrificial portion isreplaced with a conductor portion through a slit structure in theinsulating portion and in contact with the top sacrificial portion.

In some embodiments, forming the first number of divisions and thetrench structure includes repetitively patterning the stack structure toform a plurality of division patterns of different depths along thefirst direction. Each division pattern includes an initial dielectriclayer over an initial sacrificial layer at a respective top surface.Forming the first number of divisions and the trench structure alsoincludes removing a portion of the stack structure between adjacentdivision patterns.

In some embodiments, along the first direction, a width of the trenchstructure is greater than a width of the slit structure. In someembodiments, along the second direction, a length of the trenchstructure is the same as the respective stair. In some embodiments,along a vertical direction, the trench structure forms a first number ofinitial sacrificial layers in each of the adjacent divisions.

In some embodiments, the portion of the stack structure includes aportion of at least one of the adjacent divisions.

In some embodiments, each of the first number of sacrificial portions issandwiched by a pair of dielectric portions.

In some embodiments, the first number of divisions are formed prior tothe plurality of stairs.

In some embodiments, forming the insulating portion includes depositinga layer of dielectric material to fill up the trench structure, andremoving the first dielectric portion and a portion of the dielectricmaterial to expose a top surface and a side surface of a firstsacrificial portion. A top surface of the insulating portion is betweentop surfaces of adjacent first sacrificial portions.

In some embodiments, forming the top sacrificial portion, in eachdivision, includes depositing a layer of sacrificial material over thefirst sacrificial portion and the insulating portion and removing aportion of the sacrificial material to expose a side surface of theinsulating portion such that the top sacrificial portion is in contactwith the insulating portion on a top surface of the insulating portionand is disconnected from adjacent sacrificial portions.

In some embodiments, depositing the sacrificial material includesdepositing the same material as the first sacrificial portion.

In some embodiments, the method further includes forming the slitstructure in the insulating portion and in contact with the topsacrificial portion. Replacing the top sacrificial portion with aconductor portion through the slit structure includes replacing the topsacrificial portion with a conductor portion through the slit structure.

In some embodiments, forming the slit structure includes removing aportion of the insulating portion and a portion of the stack structurebetween the adjacent divisions such that the slit structure is (i) incontact with the respective top sacrificial portion, and (ii) isolatedfrom a second number of sacrificial portions in the adjacent divisions,the second number being the first number minus one.

In some embodiments, the slit structure is further (i) in contact withone or more sacrificial layers below the second number of sacrificialportions, and (ii) in contact with the second number of sacrificiallayers in contact with the sacrificial portions in each division.

In some embodiments, replacing the respective top sacrificial portion incontact with the slit structure with a conductor portion includesremoving, in each division, the top sacrificial portion through the slitstructure to form a top lateral recess, and depositing a conductormaterial to fill up the top lateral recess through the slit structure.

In some embodiments, the method further includes removing, in eachdivision, the second number of and the one or more sacrificial layers toform a plurality of lateral recesses through the slit structure, in thesame process that form the top lateral recess. In some embodiments, themethod further includes depositing the conductor material to fill up theplurality of lateral recesses through the slit structure.

In some embodiments, the method further includes forming a contactstructure in the slit structure.

In some embodiments, forming the contact structure includes depositingan insulating spacer in the slit structure and depositing a conductivematerial in the insulating spacer to fill up the slit structure.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for forming a staircase structure of amemory device, comprising: forming a first number of divisions atdifferent depths along a first direction in a stack structure and atrench structure between adjacent divisions, the stack structurecomprising interleaved sacrificial material layers and dielectricmaterial layers; forming a plurality of stairs along a second direction,wherein each of the plurality of stairs comprises the first number ofdivisions, and each of the divisions comprises a first number ofsacrificial portions, the second direction being perpendicular to thefirst direction; forming an insulating portion in the trench structure;forming a top sacrificial portion on a top surface of each of the firstnumber of divisions and in contact with the insulating portion; andreplacing the top sacrificial portion with a conductor portion through aslit structure in the insulating portion and in contact with the topsacrificial portion.
 2. The method of claim 1, wherein forming the firstnumber of divisions and the trench structure comprises: repetitivelypatterning the stack structure to form a plurality of division patternsof different depths along the first direction, each division patterncomprising an initial dielectric layer over an initial sacrificial layerat a respective top surface; and removing a portion of the stackstructure between adjacent division patterns.
 3. The method of claim 2,wherein along the first direction, a width of the trench structure isgreater than a width of the slit structure; along the second direction,a length of the trench structure is the same as the respective stair;and along a vertical direction, the trench structure forms a firstnumber of initial sacrificial layers in each of the adjacent divisions.4. The method of claim 2, wherein the portion of the stack structurecomprises a portion of at least one of the adjacent divisions.
 5. Themethod of claim 1, wherein each of the first number of sacrificialportions is sandwiched by a pair of dielectric portions.
 6. The methodof claim 1, wherein the first number of divisions are formed prior tothe plurality of stairs.
 7. The method of claim 4, wherein forming theinsulating portion comprises: depositing a layer of dielectric materialto fill up the trench structure; and removing the first dielectricportion and a portion of the dielectric material to expose a top surfaceand a side surface of a first sacrificial portion, a top surface of theinsulating portion being between top surfaces of adjacent firstsacrificial portions.
 8. The method of claim 7, wherein forming the topsacrificial portion, in each division, comprises: depositing a layer ofsacrificial material over the first sacrificial portion and theinsulating portion; and removing a portion of the sacrificial materialto expose a side surface of the insulating portion such that the topsacrificial portion is in contact with the insulating portion on a topsurface of the insulating portion and is disconnected from adjacentsacrificial portions.
 9. The method of claim 8, wherein depositing thesacrificial material comprises depositing the same material as the firstsacrificial portion.
 10. The method of claim 1, further comprisingforming the slit structure in the insulating portion and in contact withthe top sacrificial portion, and wherein replacing the top sacrificialportion with a conductor portion through the slit structure comprisesreplacing the top sacrificial portion with a conductor portion throughthe slit structure.
 11. The method of claim 10, wherein forming the slitstructure comprises removing a portion of the insulating portion and aportion of the stack structure between the adjacent divisions such thatthe slit structure is (i) in contact with the respective top sacrificialportion, and (ii) isolated from a second number of sacrificial portionsin the adjacent divisions, the second number being the first numberminus one.
 12. The method of claim 11, wherein the slit structure isfurther (i) in contact with one or more sacrificial layers below thesecond number of sacrificial portions, and (ii) in contact with thesecond number of sacrificial layers in contact with the sacrificialportions in each division.
 13. The method of claim 12, wherein replacingthe respective top sacrificial portion in contact with the slitstructure with a conductor portion comprises: removing, in eachdivision, the top sacrificial portion through the slit structure to forma top lateral recess; and depositing a conductor material to fill up thetop lateral recess through the slit structure.
 14. The method of claim13, further comprising: removing, in each division, the second number ofand the one or more sacrificial layers to form a plurality of lateralrecesses through the slit structure, in the same process that form thetop lateral recess; and depositing the conductor material to fill up theplurality of lateral recesses through the slit structure.
 15. The methodof claim 12, further comprising forming a contact structure in the slitstructure.
 16. The method of claim 13, wherein forming the contactstructure comprises: depositing an insulating spacer in the slitstructure; and depositing a conductive material in the insulating spacerto fill up the slit structure.